I. Field of the Invention
This invention relates to a process for the production of high octane motor gasoline components, and other fuels. In particular, it relates to a process for the production of high octane motor gasoline, or high octane motor gasoline components, from highly aromatic mid distillate product streams, or streams which contain high concentrations of multi-ring aromatic or hydyroaromatic compounds, whether derived from petroleum or synthetic sources, or both.
II. Background and Prior Art
Usually more than one-half of every barrel of petroleum crude that is processed in a modern refinery is converted into motor gasolines. Motor gasolines are produced from a blending pool of streams obtained from many different refinery processes, primarily from catalytic reforming and alkylation processes. Motor gasolines are constituted principally of complex mixtures of paraffins, naphthenes, olefins and aromatic hydrocarbons, which generally boil within a range of from about C.sub.5.sup.+ -430.degree. F. (20.degree.-225.degree. C.). Improved engine performance demands significantly improved motor gasoline octane requirements. Due to restrictions on the use of alkyl lead compounds, with the ultimate projection which will require prohibition of the use of such compounds in gasolines altogether, refiners are taxed in their ability to produce high octane blending components. Consequently there is a demand upon refiners to find ways and means of increasing the octane number levels of their motor gasoline pools.
Catalytic cracking, or "cat cracking," is another refinery process for producing major quantities of motor gasoline. It also suffers a major deficiency however in that it produces large quantities of highly aromatic light cat cycle oil (LCCO) due to the high temperature of the operation. The LCCO, having an API gravity of 10-15, is difficult to market for which reason it is often hydrogenated and then blended with kerosenes (a jet fuel stock) to increase its API gravity (to 30 API) so that the product can be sold as heating oil. A relatively high value product is thus used up, and depreciated in value, to make the LCCO a marketable product. LCCO, after hydrogenation, is also added to automotive diesel fuel and the product sold as automotive diesel fuel, but such manner of disposing of the LCCO is necessarily limited. Whereas conventional hydrogenation processes might be used to upgrade the LCCO this is not practical because excessive hydrogen consumption is required to increase the cetane and gravity to meet diesel specifications. On the other hand, catalytic hydrocracking processes are not efficient in producing motor gasoline blending components because these processes produce a hydrogen-rich motor gasoline component which first must be reformed before it can meet octane specifications. This, of course, adds to the cost of octane values obtained from catalytic hydrocracking processes. Additionally, conventional hydrocracking catalysts crack paraffin molecules into lower boiling paraffins which effectively reduces the octane value of the product.
Highly aromatic mid distillate streams are also available from synthetic fuel processes, e.g., coal liquification processes, and steam cracking operations for the production of olefins, e.g., steam cracker light gas oil. The product streams derived from these processes, and the problems associated with the disposition of these products is closely akin to those described above for the disposition of petroleum stocks.
In U.S. Application Ser. No. 760,894, supra, there is described a process for the production of gasoline from feeds characterized as mixtures of fused two-ring aromatic and hydroaromatic hydrocarbons which are reacted with hydrogen, over a catalyst characterized as elemental iron and one or more alkali or alkaline-earth metal components at temperatures ranging about 225.degree. C. to 430.degree. C. The feed is selectively hydrogenated and hydrocracked over the iron catalyst to produce a lower molecular weight high octane product. Whereas this process represents a meritorious advance in the state of the art much of the gasoline product resultant from this process is of lesser octane than desirable due to contamination of the product with low octane refractory components included in the feed. In addition, it is now recognized that in this process the levels of conversion of the mixed fused two-ring aromatic and hydroaromatic hydrocarbons to molecular species useful as gasoline blending components is relatively low. Many of the molecular species found in available feed streams whether from petroleum or synthetic sources, notably paraffins and naphthenes, simply do not react over the iron catalyst. Moreover, other molecular species of these mixtures, notably aromatic hydrocarbons having three rings and greater in the molecule, react in a manner detrimental to the life of the catalyst. Other species consume too much hydrogen and produce end products of no greater value, or of lesser value, than the molecular species originally present in the feed.
There presently exists a pressing need for a further improved process useful for the conversion to lower boiling hydrocarbons of higher octane levels suitable for direct use in gasoline, or as motor gasoline blending components, or diesel fuel, or both, of highly aromatic mid distillates derived from cat cracking petroleum stocks (such as light cat cycle oil; or the heavy hydrocrackate thereof), liquification of coal or the hydroconversion of heavy feeds (such as bitumen, tar sands, etc.) which contain high concentrations of multiring aromatic or hydroaromatic compounds.
III. Objects
It is, accordingly, the primary object of this invention to fill this and other needs.
In particular, it is an object of this invention to provide a process for the conversion of highly aromatic mid distillates, e.g., LCCO, or LCCO and related fuel fractions such as those obtained from synthetic and chemicals operations, or admixtures of such fuel factions, into lower boiling, high octane gasolines or motor gasoline blending components.
A specific object is to provide a process for the conversion of highly aromatic mid distillates, e.g. LCCO, or LCCO and said related fuel fractions, or admixtures of such fuel fractions, to motor gasoline of higher octane, or to high octane motor gasoline blending components.
A further, and yet more specific object, is to provide a process for the treatment of feed fractions from conventional or synthetic sources, or both, containing fused two-ring aromatic and hydroaromatic hydrocarbons of selected boiling range to coproduce, on reaction of the feed, with hydrogen, over an iron catalyst as described in U.S. Ser. No. 760,894, now U.S. Pat. No. 4,664,777 supra, a higher octane gasoline, and mid distillate useful as a diesel fuel, or diesel and/or jet fuel blending stock.
IV. The Invention
These objects and others are achieved in accordance with the process of this invention the steps of which include,
(A) in processing a sulfur-containing feed comprised of a blend rich in molecular species characterized as fused two-ring aromatic hydrocarbons, inclusive of naphthalenes, and sulfur-containing hydrocarbon compounds, boiling within a range of from about 400.degree. F. to about 600.degree. F., preferably from about 400.degree. F. to about 575.degree. F., as obtained by distillation from a wider boiling range composition, e.g., a LCCO, PA0 (B) in processing a wider boiling range sulfur-containing feed, or sulfur and nitrogen-containing feed composition constituted of fused multi-ring aromatic hydrocarbons containing two, and three or more rings in the molecule, and sulfur-containing hydrocarbon compounds. PA0 (C) in processing said wider boiling range sulfur-and nitrogen-containing feed constituted of fused multi-ring aromatic hydrocarbons containing two, and three or more rings in the molecule as defined in (B), supra, and sulfur-containing hydrocarbon compounds,
(1A) hydrogenating said feed over a hydrogenation catalyst at hydrogenation conditions sufficient to remove sulfur, preferably to 10 parts, per million parts (ppm), by weight of feed, or less and saturate one ring of said molecular species, inclusive of naphthalenes, but insufficient to saturate the second ring of said molecular species, PA1 (1AA) contacting and reacting in an optional, but preferred step, the hydrogenated product from (1A), supra, as a feed with a hydroisomerization catalyst at conditions sufficient for rearrangement of the molecular species of said hydrogenated product to form indanes and other molecular species, and increase the concentration of indanes and other molecular species in said product, and then PA1 (2A) contacting the hydrogenated product from (1A) or 1AA), supra, as a feed in the presence of hydrogen, over a catalyst comprised of elemental iron and one or more alkali or alkaline-earth metals components at a temperature ranging from about 225.degree. C. (437.degree. F.) to about 430.degree. C. (806.degree. F.), preferably from about 250.degree. C. (482.degree. F.) to about 400.degree. C. (752.degree. F.), and hydrogen partial pressure ranging generally from about 0 pounds per square inch gauge (psig) to about 1000 psig, preferably from about 100 psig to about 600 psig to selectively further hydrogenate and crack said previously hydrogenated fused two-ring aromatic hydrocarbon (or molecular species one ring of which was previously hydrogenated with minimal hydrogenation of the second ring of said species) to produce lower molecular weight, high octane components suitable per se as gasoline or suitable for use as a motor gasoline blending component; or, PA1 (1B) splitting the feed into two liquid feed fractions, (a) a first feed fraction constituting a blend rich in fused two-ring aromatic hydrocarbons, inclusive of naphthalenes, boiling within a range of from about 400.degree. F. to about 600.degree. F., preferably from about 400.degree. F. to about 575.degree. F., and (b) a second feed fraction constituting a blend rich in fused multi-ring aromatic hydrocarbons having three or more rings in the molecule and boiling within a range of from about 600.degree. F. to about 750.degree. F., preferably from about 575.degree. F. to about 650.degree. F., PA1 (2B) hydrogenating over a hydrogenation catalyst at hydrogenation conditions said first feed fraction at the conditions defined in (1A), supra, sufficient to remove sulfur, preferably to 10 ppm by weight, or less, and saturate one ring of the fused two-ring aromatic hydrocarbon species, inclusive of naphthalenes, but insufficient to saturate the second ring of said molecular species, PA1 (3B) contacting said hydrogenated first feed fraction obtained form step (2B) or (2BB) in the presence of hydrogen, over an iron catalyst as defined in A (2A) at the conditions defined in A (2A) to selectively hydrogenate and crack said previously hydrogenated fused two-ring aromatic hydrocarbon to produce lower molecular weight, higher octane components suitable per se as gasoline or a motor gasoline blending component, and PA1 (4B) contacting said second feed fraction rich in fused multi-ring aromatic hydrocarbons containing three or more rings to the molecule as defined in 1B (b) over a hydrogenation catalyst, in the presence of hydrogen, at temperature and pressures sufficient to hydrogenate the fused multi-ring aromatic hydrocarbon components and produce molecular components directly useful as blending components for diesel or heating oil; or suitable as feedstock for recycle to a "cat cracker" for conversion to lower molecular weight lighter boiling components to produce motor gasoline or motor gasoline blending components; or suitable as a feedstock for conversion over a hydrocracking catalyst, in the presence of hydrogen at temperature and pressure sufficient to hydrocrack the fused multi-ring aromatic hydrocarbon components and product lower molecular weight lighter boiling components useful as motor gasoline or motor gasoline blending components; or PA1 (1C) hydrogenating over a hydrogenating catalyst at hydrogenation conditions, the whole feed at conditions sufficient to remove sulfur and nitrogen, particularly the latter, preferably to 10 ppm by weight, or less, and saturate one ring of the two-ring molecular species, but insufficient to saturate the second ring of said molecular species, of the fused two-ring aromatic hydrocarbons components of said mixture of hydrocarbons, inclusive of naphthalenes, PA1 (2C) hydrocracking over a hydrocracking catalyst at hydrocracking conditions, the whole of the product liquid, previously hydrogenated as defined in (1C), supra, to crack fused multi-ring aromatic hydrocarbons containing three or more rings to the molecule and produce lower molecular weight lower boiling components, PA1 (3C) separating, suitably and preferably by distillation, the liquid product of said hydrocracking step as defined in (2C), supra, into blends which include PA1 (4C) contacting and reacting said blend rich in fused two-ring aromatic hydrocarbons as defined in (3C) (i), supra, with hydrogen, over a catalyst comprised of elemental iron and one or more alkali or alkaline-earth metals components at a temperature ranging from about 225.degree. C. (437.degree. F.) to about 430.degree. C. (806.degree. F.), preferably from about 250.degree. C. (482.degree. F.) to about 400.degree. C. (752.degree. F.), and hydrogen partial pressure ranging generally from about 0 psig to about 1000 psig, preferably from about 100 psig to about 600 psig, to selectively hydrogenate and crack said previously hydrogenated fused two-ring aromatic hydrocarbons to produce lower molecular weight, ultra high octane components suitable per se as gasoline or suitable as a gasoline blending component, and PA1 (5C) contacting and reacting said blend rich in fused multi-ring hydrocarbons containing three or more rings to the molecule as defined in (3C) (ii), supra, over
(2BB) contacting and reacting in an optional, but preferred step, the hydrogenated product from (2B), supra, as a feed with a hydroisomerization catalyst at conditions sufficient for rearrangement of the molecular species of said hydrogenated product to form indanes and other molecular species, and increase the concentration of indanes and other molecular species in said product, and then PA2 (i) a blend rich in fused two-ring aromatic hydrocarbons boiling within a range of from about 400.degree. F. to about 600.degree. F., preferably from about 400.degree. F. to about 575.degree. F., and PA2 (ii) a blend rich in fused multi-ring hydrocarbons containing three or more rings to the molecule boiling within a range of from about 600.degree. F. to about 750.degree. F., preferably from about 575.degree. F. to about 650.degree. F., then PA2 (i) a hydrocracking catalyst at hydrocracking conditions, to crack the fused multi-ring aromatic hydrocarbon components and produce lower molecular weight lower boiling components suitable as motor gasoline, or motor gasoline blending components, or PA2 (ii) a hydrogenation catalyst at hydrogenation conditions, to hydrogenate the fused multi-ring aromatic hydrocarbon components and produce molecular components suitable as diesel, or diesel blending components, or PA2 (iii) a catalytic cracking catalyst at catalytic cracking conditions to crack the fused multi-ring aromatic hydrocarbon components and produce molecular components suitable as motor gasoline, or motor gasoline blending components.
The present invention in its more general aspects, or aspects as defined in (A), or in the specific combination of steps defined by (B) 2B(2BB), wherein a low boiling feed is hydrogenated and optionally hydrocracked, and the hydrogenated, or hydrogenated/ hydrocracked, product processed over an iron catalyst, is based in part on the discovery that the iron catalyst selectively ring opens partially hydrogenated fused two-ring aromatic hydrocarbon compounds while leaving paraffins and decalins essentially unconverted; that the iron catalyst has poor hydrogenation activity for hydrogenating fused two-ring aromatic compounds; and that some of the higher boiling fused multi-ring aromatic hydrocarbons substantially reduce the activity of the iron catalyst over time, this adversely affecting the activity maintainanced or life of the iron catalyst. For example, an LCCO feed contains relatively high concentration of naphthalenes, inclusive of naphthalene and alkyl substituted naphthalenes; generally naphthalenes containing from 1 to about 4 methyl groups in the molecule. The iron catalyst, it has now been found, will not effectively "ring-open" naphthalenes, and hence the reaction of a feed high in naphthalenes over an iron catalyst does not achieve the desired higher conversion levels possible with other types of feed components, e.g., tetralins. Moreover, the presence of the unreacted naphthalenes in the product suppresses the octane value of the product, and its octane is less than would be possible if more of the naphthalenes were ring-opened over the iron catalyst. Further it has been found that feeds, e.g., LCCO feeds, boiling above about 575.degree. F., and especially above about 600.degree. F., contain fused multi-ring aromatic hydrocarbons having greater than two rings in the molecule which react to reduce the activity maintainance of the iron catalyst because many of these compounds form other reaction product which for different reasons adversely affect the catalytic iron surface of the catalyst. In accordance with the process of this invention as defined in (A), or in the specific combination of steps defined by steps (B) 2B(2BB) therefore, feed streams rich in fused two-ring aromatic hydrocarbons, boiling below about 600.degree. F., preferably below about 575.degree. F., containing high concentrations of naphthalenes are first hydrogenated over conventional hydrotreating catalysts at conventional hydrogenating conditions, to desulfurize the feed and convert the naphthalenes to tetralins, and in an optional hydroisomerization step tetralins can be converted to other molecules by rearrangement, the molecularly rearranged molecules producing lower yields of methane when subsequently ring opened over the iron catalyst. The iron catalyst is thus employed in a subsequent step to ring-open the tetralins, and rearranged molecules, and convert the tetralin-enriched product or product enriched in tetralin and rearranged molecular species to alkylbenzenes; a product of higher octane than would otherwise have been possible to produce without said hydrogenation step. The iron catalyst in terms of its intrinsic activity is thus a poor hydrogenation catalyst per se, but readily ring-opens the saturated ring of tetralin without cracking the unsaturated ring, or aromatic portion of the molecule.
In the step of reacting a predominantly fused two-ring aromatic feed fraction, e.g., an LCCO feed fraction, over the iron catalyst two primary type operations are attractive: the first, a low pressure operation generally conducted at hydrogen pressures ranging from about 100 psig to about 450 psig, preferably from about 250 psig to about 350 psig, and the second a high pressure operation conducted at hydrogen pressures ranging from about 500 psig to about 1000 psig, preferably from about 500 psig to about 650 psig. In both, prior to reaction of the feed over the iron catalyst, the feed is preferably hydrogenated and reacted over a conventional hydrogenation catalyst at conventional hydrogenation conditions to remove sulfur, preferably to 10 ppm, or less, and then optionally hydrocracked; and, in the process wherein the product as a feed is to be treated over the iron catalyst at low pressures it is hydrogenated sufficient to convert the naphthalenes of the feed to tetralins, because a low pressure the iron catalyst does not have sufficient hydrogenation activity to hydrogenate the naphthalenes.
The iron catalyst, as disclosed in Application Ser. No. 760,894 now U.S. Pat. No. 4,664,777, supra, has the unique ability to ring open fused two-ring aromatic hydrocarbons to form high octane alkylbenzenes. The iron catalyst however also has the propensity to demethylate the alkylbenzenes to form methane and ultimately BTX, viz. benzene, toluene and xylenes; and undesirable result since excessive hydrogen is consumed, and the product reduced in value. Different types of operation are possible to reduce the formation of methane, one of which requires operation of the reactor containing the iron catalyst at low hydrogen pressure, and the other operation of the reaction containing the iron catalyst at high hydrogen pressures. Each offers certain advantages.
In low pressure operation, the hydrogenation of the feed over the hydrogenation catalyst is conducted at temperature, pressure and at hydrogen rate sufficient to reduce the level of sulfur to about 10 ppm, or less, and naphthalenes to about 5 weight percent, or less, preferably below about 3 weight percent, because the presence of naphthalenes in greater amounts inhibits the activity of the iron catalyst to ring open tetralins. Further, the passage of unreacted naphthalenes through the reactor containing the iron catalyst will result in a loss in yield of the highly desirable, high octane alkylbenzenes.
In reacting a hydrogenated feed rich in fused two-ring aromatic hydrocarbons over an iron catalyst at 350.degree. C., 150 psig, it has been found that the yield of methane lines out at about 6 to 8 weight percent in achieving essentially 100 weight percent conversion of the tetralins on a once-through basis. At 330.degree. C., 150 psig, the yield of methane when utilizing a similar feed lines out at about 2 to 3 weight percent with a tetralin conversion level of about 30 to 40 weight percent. In the latter case the product can be recycled to the reactor containing the iron catalyst to ultimately achieve essentially total conversion of the tetralin to alkylbenzenes with lower methane production than in the former case. This offers advantages, but requires a trade off between reactor capacity and methane formation.
In high pressure operations, a feed with fused two-ring aromatic hydrocarbons, inclusive of naphthalenes in concentration ranging from about 5 percent to about 25 percent, preferably from about 10 percent to about 20 percent, based on the weight of the feed, can be reacted over the iron catalyst at hydrogen pressures ranging from about 500 psig to about 1000 psig, preferably about 500 psig to about 650 psig, without excess methane formation. Methane yield is directly related to the hydrogenation activity of a catalyst, and albeit the iron catalyst is a poor hydrogenation catalyst at low hydrogen partial pressures, it improves sufficiently at high hydrogen partial pressures to hydrogenate naphthalenes. At low hydrogen pressures, e.g., 150 psig, data have shown that the iron catalyst has very limited capability to hydrogenate fused two-ring aromatics. However, at high hydrogen pressures the fused two-ring aromatics can be hydrogenated via use of the iron catalyst, but excessive amounts of methane are produced. Methane yields in the range of about 10 weight percent to 25 weight percent are produced at e.g., 500-1000 psig and 350.degree. C. with a feed composition rich in tetralins, but containing less than 3 weight percent naphthalenes. It has been found however that by only partially hydrogenating the naphthalenes component of an LCCO feed in the hydrogenation reactor, the naphthalenes remaining in the product will inhibit or suppress methane formation on contact and reaction of the naphthalene-containing feed over the iron catalyst. An LCCO feed derived from petroleum thus normally contains about 60 to 70 weight percent naphthalenes, a portion of which can be hydrogenated over a conventional hydrogenation catalyst at conventional hydrogenation conditions to leave a concentration of naphthalenes in the product ranging from about 5 percent to about 25 weight percent, preferably 10 weight percent to about 20 weight percent, which product can be used as a feed to the reactor containing the iron catalyst.
Methane yield, in summary, is thus directly related to the hydrogenation function of the iron catalyst, which increases with increasing hydrogen pressure. The presence of naphthalenes however suppresses the formation of methane, and hence the naphthalenes can be used to suppress methane formation when the hydrogen pressure on the system employing the iron catalyst is increased. This effect it is believed, while not completely understood, can be explained; at least in part. The naphthalenes are believed to absorb on the hydrogenation sites required for formation of tetralins, and demethylation of the aromatic hydrocarbon molecules. By absorbing naphthalene to limit these sites, sites are no longer available for demethylation and hence methane yield is reduced. sufficient sites remain however for ring opening of the tetralins to produce alkylbenzenes.
In a second embodiment, as described in (B), supra, a wider boiling range sulfur and nitrogencontaining feed or feed boiling within a range of from 400.degree. F. to about 750.degree. F., preferably 400.degree. F. to about 650.degree. F., is split into two liquid components, (1) a first rich in fused two-ring aromatic hydrocarbons boiling below about 600.degree. F., preferably below about 575.degree. F., which first is conventionally hydrogenated, and then reacted over the iron catalyst to selectively crack the fused two-ring aromatic hydrocarbons, and (2) a second liquid rich in fused multi-ring aromatic hydrocarbons containing three or more rings in the molecule which is hydrogenated in conventional manner. A greater amount of higher octane gasoline is produced by splitting the feed in this manner, and then reacting the two liquid product fractions as described than would be possible by conventionally hydrocracking the whole feed. In treating the low boiling fraction in this manner the same benefits are obtained as discussed in connection with the treatment as defined in (A), supra. Added benefits are obtained, and difficulties avoided, by then hydrogenating the higher boiling liquid fraction over a conventional hydrogenating catalyst in conventional manner. The hydrogenated product contains molecular components directly useful as blending components for diesel fuel or heating oil. Alternately the hydrogenated product can be converted in a cat cracker over a cat cracking catalyst at cat cracking conditions to lower boiling, lower molecular weight components suitable as motor gasoline or motor gasoline blending components. Or, the hydrogenated product can be conventionally hydrocracked at hydrocracking conditions over a hydrocracking catalyst, in the presence of hydrogen, to produce motor gasoline or motor gasoline blending components.
The portion of the conventional LCCO fraction which boils above 575.degree. F., particularly above 600.degree. F., contains high concentrations of methylphenanthrenes. This fraction, generally 65 to 70 weight percent of the total of the feed components boiling above 575.degree. F., can thus be hydrocracked suitably over a conventional hydrocracking catalyst to produce light gas (C.sub.4.sup.-) and methylnaphthalenes, the latter of which can be recycled and reacted over the iron catalyst to produce alkylbenzenes. In another option the methylphenanthrenes can be partially hydrogenated and recycled to the "cat cracker" for further conversion to motor gasoline or fully hydrogenated to produce high octane diesel blending components. Data have shown that the activity maintainance of the iron catalyst is greatly improved when the final boiling point of the fused two-ring aromatic feed is reduced to 600.degree. F., preferably 575.degree. F. Typically, treating a 400.degree./575.degree. F. LCCO feed converts greater than 95 weight percent of the fused two-ring aromatic hydrocarbon compounds in the LCCO without substantial debit to the process in terms of alkylbenzene production, while simultaneously the activity maintainance of the catalyst is greatly improved.
In a third embodiment, or embodiment as defined by (C), a wide boiling range sulphur-containing, and nitrogen-containing feed rich in fused multi-ring aromatic and hydroaromatic hydrocarbons containing two and three, or more, rings in the molecule, i.e., boiling within a range of from about 400.degree. F. to about 750.degree. F., preferably from about 400.degree. F. to about 650.degree. F., is processed in a manner which will convert a maximum amount of the feed components to high octane motor gasoline, or high octane motor gasoline components, mid-distillates and other fuels. The feed is conventionally hydrogenated, the liquid product therefrom conventionally hydrocracked, and the hydrogenated/hydrocracked product then split, suitably by distillation, into fractions other than C.sub.4.sup.- and light gas, and low octane gasoline suitable as a reformer feed, two liquid fractions, a first fraction rich in fused two-ring aromatic hydrocarbons boiling within a range of from about 400.degree. F. to about 600.degree. F., preferably 400.degree. F. to about 575.degree. F., and second fraction rich in fused multi-ring aromatic hydrocarbons having three or more rings to the molecule, boiling within a range of from about 600.degree. F. to about 750.degree. F., preferably 575.degree. F. to about 650.degree. F. The first fraction which is rich in fused two-ring aromatic hydrocarbons is then reacted over an iron catalyst, as previously described, and the second fraction which is rich in fused multi-ring aromatic hydrocarbons having three or more rings in the molecule is (i) then reacted over a conventional hydrocracking catalyst at conventional hydrocracking conditions, as previously described, to produce gasoline of improved octane in high yield, (ii) hydrogenated to produce diesel or high cetane blending products, or (iii) reacted over a conventional catalytic cracking catalyst at conventional catalytic cracking conditions to produce motor gasoline, or motor gasoline blending components.
To summary, three process schemes are thus generally useful in the practice of this invention, dependent on the nature of the available feed. In accordance with the first process scheme, (A) supra, a narrow boiling range feed boiling within a range of about 400.degree. F./600.degree. F., preferably 400.degree. F./575.degree. F., rich in fused two-ring aromatic hydrocarbons neither ring of which is hydrogen saturated, e.g., naphthalenes, is hydrogenated in a first step over a hydrogenation catalyst to desulfurize the feed and hydrogen saturate one of the unsaturated rings, but not the other, e.g., to produce tetralins. The product of the hydrogenation reaction is then stripped to remove the H.sub.2 S generated in the first stage, and the product liquid then reacted in a second stage over the iron catalyst. In an optional step, the hydrogenated product can be hydroisomerized over a hydroisomerization catalyst to effect molecular rearrangement of the hydrogenated product so that on reaction of the hydroisomerized product over the iron catalyst lower yields of methane will be formed. The molecular arrangement can be (1) the formation of indanes from tetralins, (2) the formation of indanes or tetralins, or both, with repositioned methyl and other alkyl substituents, or (3) other yet unidentified species, which can be ring opened over the iron catalyst at lower methane yields. Ideally, it is desirable to maximize the amount of tetralins (or indanes) in the feed to the reactor containing the iron catalyst since the tetralin molecules are ring opened to form gasoline. Conversely, it is desirable to minimize the amount of naphthalenes, since these compounds are minimally hydrogenated over the iron catalyst, and indeed are absorbed on the iron catalyst to inhibit its ability to convert the tetralin molecules. in addition, it is preferable to limit hydrogenation of the naphthalenes to decalins since decalins are not converted over the fused iron catalyst and indeed are adsorbed on reaction sites to limitt the ring opening ability of the catalyst. The front end boiling point of the feed is maintained at 400.degree. F. to avoid diluting the gasoline product with low octane unconverted components from the feed (e.g., paraffins), and the final boiling point is limited to 600.degree. F., or 575.degree. F., to exclude compounds which suppress the life of the iron catalyst. Thus, in conducting the hydrogenation reaction at low hydrogen partial pressures, i.e., 100 psig to 450 psig, the boiling range is limited and the naphthalene level is reduced to 5 percent or less, preferably 3 percent or less, based on the weight of the feed. Conversely, in conducting the hydrogenation reaction at high hydrogen partial pressures, i.e., 500 psig to 1000 psig, the naphthalene level is maintained at from about 10 percent to about 25 percent, based on the weight of the feed. The sulfur level is reduced to 10 ppm or less, based on the weight of the feed.
The hydrogenation catalyst is generally characterized as one wherein one or more Group VIB or Group VIII metals of the Periodic Table of the Elements (E. H. Sargent & Co., Copyright 1962 Dyna Slide Co.) is dispersed upon a porous inorganic oxide support, suitably alumina. Exemplary of such metals are molybdenum, tungsten, cobalt, nickel, and admixtures of such metals, suitably nickel-molybdenum, cobalt-molybdenum or nickelcobalt molybdenum.
Suitable hydrogenation conditions are defined in Table 1 as follows:
TABLE 1 ______________________________________ Hydrogenation Conditions Typical Range Preferred Range ______________________________________ Temperature, .degree.F. 550-800 600-750 Pressure, psig 200-2000 500-1500 LHSV, V/V/Hr. 0.1-10 0.5-2.0 Hydrogen Rate, SCF/B 500-10,000 1000-5000 ______________________________________
The hydrogenated liquid product from the hydrogenation reactor, after stripping to remove the H.sub.2 S, is preferably contacted in a second reactor over the iron catalyst at temperature ranging from about 225.degree. C. (437.degree. F.) to about 430.degree. C. (752.degree. F.), more preferably from about 250.degree. C. (482.degree. F.) to about 400.degree. C. (752.degree. F.) and more preferably from about 300.degree. F. to about 375.degree. C., and at hydrogen partial pressures ranging from about 0 psi to about 1200 psi, preferably from about 100 psi to about 500 psi, sufficient to ring open said fused multi-ring aromatic hydrocarbon compounds, or fused multi-ring hydroaromatic hydrocarbon compounds, or both, and produce higher boiling components suitable as motor gasoline, or motor gasoline blending components.
Some positive pressure of hydrogen is necessary in conducting reactions of the feed over the iron catalyst. The combination of temperature and hydrogen partial pressure are preferably such that most of the feed, at reaction conditions, is in vapor phase. Temperatures above about 430.degree. C. (806.degree. F.) generally should not be employed because excessive temperature causes cracking of the feed, which can lower liquid yields. At temperatures below about 225.degree. C. (437.degree. F.) on the other hand, the rate of reaction is generally too slow as to be practical. Total pressures are not critical, but generally range from about 0 psig to about 1500 psig, preferably from about 100 psig to about 1000 psig. Treat gas rates, based on hydrogen, range from about 500 to about 10,000 SCF/B, preferably from about 1000 to about 5000 SCF/B. Space velocities range generally from about 0.05 LHSV to about 20 LHSV, preferably from about 0.2 LHSV to about 5 LHSV.
The iron catalyst is constituted of elemental iron, modified with one or more alkali or alkaline-earth metals, or compounds thereof, sufficient to produce on contact with a feed at reaction conditions ring opening of the fused two-ring aromatics and hydroaromatics of the feed without significant cracking of paraffins or naphthenic hydrocarbon components of the feed. Preferably iron is present in the catalyst as the major component, or major metal component. The catalyst may be bulk (unsupported) iron, or iron dispersed upon a support. The bulk iron catalyst is preferred and it may be employed as essentially metallic iron in bulk, or as a bulk iron promoted or modified with alkali or alkaline-earth metals, or metal oxides such as sodium, potassium, cesium, magnesium, calcium, barium, or the like. The active iron catalyst, when a bulk iron catalyst, is preferably one which contains at least 50 percent elemental iron, preferably from about 70 percent to about 98 percent elemental iron, based on the weight of the catalyst. The iron catalyst, when a catalyst wherein the iron is distributed or dispersed upon a support, contains at least about 0.1 percent iron (measured as elemental iron), preferably from about 0.1 percent to about 50 percent iron, and more preferably from about 5 percent to about 25 percent iron, based on the total weight of the catalyst, and the supported metallic component, exclusive of the support component, or components, contains at least 50 percent iron (measured as elemental iron), and preferably from about 70 percent to about 98 percent iron.
A bulk or unsupported fused iron catalyst is preferred. A fused iron catalyst is one fused by heating and melting the iron, preferably with an alkali or alkaline-earth metal, or metals, the alkali or alkaline-earth metal, or metals, generally being present in concentrations ranging from about 0.01 percent to about 10 percent, preferably from about 0.2 percent to about 4 percent, based on the total weight of catalyst. Sodium, potassium, cesium, magnesium, calcium, and barium are the preferred alkali or alkaline-earth metals. Aluminum, principally as an oxide (Al.sub.2 O.sub.3), or compound thereof is also a preferred promoter, or modifier, of the fused iron, and it is preferably contained in the catalyst in concentration ranging from about 0.01 percent to about 20 percent, more preferably from about 0.5 percent to about 5 percent calculated as aluminum oxide (Al.sub.2 O.sub.3) based on the total weight of the catalyst. Other metals may also be used as promoters and/or modifiers, such metals including rhenium, nickel, cobalt, palladium, platinum, and copper. Such metals may be added to the catalyst alone or admixed one metal with another, or with other metals.
The iron based catalyst, as suggested, may also be supported; preferably upon an inorganic oxide support. Supports include, but are not limited to, the oxides of aluminum, silicon, boron, phosphorous, titanium, zirconium, calcium, magnesium, barium, and mixtures of these and other components. Other supports may include clays, such as bentonite, zeolites, and other alumino-silicate materials, e.g., montmorillionite. Additional supports may be selected from the group of refractory carbides and nitrides of the transition metals of Groups IVB, VB, VIB, VIIB, and Group VIII iron group metals. Alumina, magnesia, and mixtures of alumina and magnesia are preferred supports. The iron based catalysts are prepared by methods which include precipitation, coprecipitation, impregnation, vapor deposition, and the formation of metal complexes (i.e., metal carbonyl, etc.) and the like. The impregnation of a porous inorganic oxide support, such as alumina, with a solution of an iron salt with subsequent drying, calcination and reduction of the supported iron catalyst by contact and treatment of the catalyst with hydrogen or hydrogen and ammonia, or ammonia in admixture with another reducing gas, or gases, has been found to provide a highly active catalyst for selectively hydrogenating and hydrocracking the fused multi-ring aromatics and hydroaromatics to produce lower boiling, high octane components for use in motor gasoline. Impregnation of the support with iron, or iron and other metal promoters or modifiers, by the incipient wetness technique, or technique wherein the iron is contained in solution in measured amount and the entire solution absorbed into the support, subsequently dried, calcined, and activated is preferred. The supported iron catalyst is promoted or modified with alkali or alkaline-earth metals, or metal oxides such as sodium, potassium, cesium, magnesium, calcium, barium, or the like. The alkali or alkaline-earth metal, or metals or compounds thereof are generally employed in concentrations ranging from about 0.01 percent to about 10 percent, preferably from about 0.2 percent to about 4 percent, based on the total weight of metal, exclusive of the weight of the support. Sodium, potassium, cesium, magnesium, calcium, and barium, are the preferred alkali or alkaline-earth metals. Aluminum, principally as an oxide, or compound thereof, is also a preferred promoter, or modifier, and it is preferably employed in the catalyst in concentration ranging from about 0.01 percent to about 20 percent, more preferably from about 0.5 percent to about 5 percent, calculated as aluminum oxide (Al.sub.2 O.sub.3), based on the total weight of metal, exclusive of the weight of the support. Rhenium, nickel, cobalt, palladium, platinum, and copper metals, or compounds thereof, can also be added to the catalyst as promoters or modifiers, these metals generally being added in concentrations ranging from about 0.01 percent to about 10 percent, preferably in concentration ranging from about 0.5 percent to about 2.5 percent, based on the weight of the supported component, exclusive of the weight of the support. After impregnation of the support, the metal impregnated support is dried generally at temperatures ranging from about 149.degree. F. (65.degree. C.) to about 536.degree. F. (280.degree. C.), preferably from about 176.degree. F. (80.degree. C.) to about 230.degree. F. (110.degree. C.), in circulating air, vacuum or microwave oven. The calcination is suitably conducted at temperatures ranging from about 572.degree. F. (300.degree. C.) to about 1202.degree. F. (650.degree. C.), preferably from about 842.degree. F. (450.degree. C.) to about 1022.degree. F. (550.degree. C.). The iron catalysts can be reduced, activated, or reactivated by contact with hydrogen, by sequential contact with hydrogen and ammonia or reduced and activated by contact with an admixture of ammonia and hydrogen or by contact with an admixture of ammonia and another reducing gas or gases.
Additional process schemes involve the processing of a wider boiling range feed, the first, (B), supra, requiring splitting the feed into two fractions, a first 400.degree. F./600.degree. F. feed fraction, or 400.degree. F./575.degree. F. feed fraction, which is processed in identical manner as the narrow boiling range feed, and a second feed fraction boiling at 600.degree. F.+, preferably 575.degree. F.+, which is hydrogenated to directly produce diesel fuel or heating oil; or a product suitable as a feed to a cat cracker to produce lower boiling components suitable as motor gasoline or motor gasoline blending components; or a product suitable as a feed to a hydrocracker to produce motor gasoline or motor gasoline blending components.
In another scheme for treating a wide boiling range feed containing fused multi-ring aromatic hydrocarbons having two, three and more rings to the molecule, the whole of the feed as described in (C), supra, is hydrogenated (1C), the liquid product therefrom is then hydrocracked (2C), and the liquid product then separated into two fractions (3C), a 400.degree. F./600.degree. F., preferably a 400.degree. F./575.degree. F. fraction, which is selectively hydrocracked over an iron catalyst (4C) and a 600.degree. F./750.degree. F., preferably a 575.degree. F./650.degree. F. fraction, which is hydrocracked, hydrogenated, or catalytically cracked (5C). The fraction which is hydrogenated is hydrogenated with a conventional hydrogenation catalyst at conventional hydrogenation conditions similar to those described in Table 1. In this reaction, the component of the feed containing the fused two-ring aromatics neither of which is saturated, e.g., naphthalenes, are partially hydrogenated to produce fused two-ring aromatics one ring of which is saturated and the other not saturated, e.g., tetralins. The feed is desulfurized and denitrogenated, and the product of the hydrogenation reaction as a feed, is then hydrocracked over a conventional hydrocracking catalyst at hydrocracking conditions as defined in Table 2. In such hydrocracking reaction, predominantly the fused multi-ring aromatics containing three or more rings are hydrocracked to lower molecular weight components. The product of this reaction is then separated into fractions which include two liquid fractions one a 400.degree. F./600.degree. F. or 400.degree. F./575.degree. F. fraction which is selectively ring opened over an iron catalyst (4C), and the second a 600.degree. F./760.degree. F. or 575.degree. F./650.degree. F. fraction which is (5C) (i) hydrocracked over a conventional hydrocracking catalyst at conditions as defined in Table 2; (5C) (ii) hydrogenated over the same catalyst at conditions shown in Table 1 and in the presence of minimal H.sub.2 S, or (5C) (iii) catalytically cracked over a conventional catalytic cracking catalyst. Tetralins are the primary molecules that are converted over the iron catalyst, at conditions previously defined to produce gasoline and gasoline blending components.
In ring-opening the tetralins of the feed over the iron catalyst in accordance with step (4C), the gasoline or gasoline blending components produced on distillation are of ultra high octane, typically ranging from about 108 to 112 RONC. This compares favorably to the octane of the hydrocrackate prepared in step (2C) which, even after reforming is about 100 RONC. Thus, it may be preferable to provide a separate distillation column in association with step (4C) to split or distill the product to produce an ultra high octane motor gasoline as well as an unconverted higher boiling stream (400.degree. F..sup.+) which can be recycled over the iron catalyst. The unconverted feed is suitable as a diesel fuel (and has a cetane number ranging from about 35 to 45).
Gasoline, gasoline blending components, mid-distillates and other fuels are produced in the second stage hydrocracker on contact of the hydrocracking catalyst at hydrocracking conditions with the feed consisting essentially of fused multi-ring aromatic hydrocarbon containing three or more rings in the molecule. Diesel or diesel blending components are the primary products.
For conducting hydrocracking operations, preferred hydrocracking catalysts are constituted generally of a crystalline zeolite cracking base upon which a minor proportion of a Group VIII metal hydrogenating components is deposited. Additional hydrogenated components may be selected from Group VIB for incorporation with the zeolite base. The zeolite cracking bases, often referred to as molecular sieves, are usually composed of silica, alumina and one or more exchangeable cations such as sodium, hydrogen, magnesium, calcium, rare earth metals, and the like. They are further characterized by crystal pores of relatively uniform diameter between about 4 and 14 Angstrom units. It is preferred to employ zeolites having a relatively high silica/alumina mole ratio between about 3 and 12, and even more preferably between about 4 and 8. The naturally occurring zeolites are normally found in a sodium form, an alkaline earth metal form, or mixed forms. Suitable zeolites found in nature include for example mordenite, stilbite, heulandite, ferrierite, dachiardite, chabazite, erionite, and faujasite. Suitable synthetic zeolites include for example the B, X, Y, and l crystal types or synthetic forms of the natural zeolites noted above, e.g., synthetic faujasite and mordenite. The preferred zeolites are those having crystal pore diameters between about 8-12 Angstrom units, wherein the silica/alumina mole ratio is about 4 to 6. A prime example of a zeolite falling in this preferred group is synthetic Y molecular sieve.
The synthetic zeolites are nearly always prepared first in the sodium form. In any case, for use as a cracking base it is preferred that most or all of the original zeolitic monovalent metals be ion-exchanged with a polyvalent metal and/or with an ammonium salt followed by heating to decompose the ammonium ions associated with the zeolite, leaving in their place hydrogen ions and/or exchange sites which have actually been "decationized." Y zeolites of this nature are more particularly described in U.S. Pat. No. 3,130,006.
Mixed polyvalent metal-hydrogen zeolites may be prepared by ion-exchanging first with an ammonium salt, then partially back exchanging with a polyvalent metal salt and then calcining. In some cases, as in the case of synthetic mordenite, the hydrogen forms can be prepared by direct acid treatment of the alkali metal zeolites. The preferred cracking bases are those which are at least about 10 percent, and preferably at least 20 percent, metal-cation-deficient, based on the initial ion-exchange capacity. A specifically desirable and stable class of zeolites are those wherein at least about 20 percent of the ion-exchange capacity is satisfied by hydrogen ions.
The active metals employed in the hydrocracking catalysts as hydrogenation components are those of Group VIII, i.e., iron, cobalt, nickel, ruthenium, rhodium, palladium, osmium, iridium, and platinum. In addition to these metals, other promoters may also be employed in conjunction therewith, including the metals of Group VIB, e.g., molybdenum and tungsten. The amount of hydrogenating metal in the catalyst can vary within wide ranges. Generally, any amount between about 0.05 percent and 30 percent by weight may be used. In the case of the noble metals, it is normally preferred to use about 0.05 to about 2 weight percent. The preferred method for incorporating the hydrogenating metal is to contact the zeolite base material with an aqueous solution of a suitable compound of the desired metal wherein the metal is present in a cationic form. Following addition of the selected hydrogenating metal or metals, the resulting catalyst powder is then filtered, dried, pelleted with added lubricants, binders or the like if desired, and calcined in air at temperatures of, e.g., 700.degree.-1200.degree. F. in order to activate the catalyst and decompose ammonium ions. Alternatively, the zeolite component may first be pelleted, followed by the addition of the hydrogenating component and activation by calcining. The foregoing catalysts may be employed in undiluted form, or the powdered zeolite catalyst may be mixed and copelleted with other relatively less active catalysts, diluents or binders such as alumina, silica gel, silica-alumina cogels, activated clays and the like in proportions ranging between 5 and 90 weight percent. These diluents may be employed as such or they may contain a minor proportion of an added hydrogenating metal such as a Group VIB and/or Group VIII metal.
Suitable hydrocracking conditions for conducting the hydrocracking operation can very within the ranges given in Table 2.
TABLE 2 ______________________________________ Hydrocracking Conditions Typical Range Preferred Range ______________________________________ Temperature, .degree.F. 450-850 500-775 Pressure, psig 500-4000 1000-3000 LHSV, V/V/Hr 0.2-20 0.5-10 Hydrogen Circulation, 2000-20,000 2000-10,000 SCF/B ______________________________________
In conducting the process described by reference to (C), two-ring aromatics are hydrogenated and hydroisomerized over conventional hydrocracking catalysts to produce molecular rearrangement of tetralin with low yields of methane, and this product as a feed is then ring-opened over the fused iron catalyst. In the process steps described by reference to (A) and (B) it is desirable to molecularly rearrange the tetralin at moderate conditions to avoid hydrocracking reactions, because paraffins, which are present are also hydrocracked to form lower molecular species which contaminate the product and lower product octane. The desired molecular rearrangement can be readily accomplished by the use of a small bed of conventional hydrocracking catalyst, e.g., HC-18 (Pd zeolite), in front or in advance of the bed of iron catalyst, operated at the same conditions as the bed of iron catalyst. Alternately, other catalysts can be so employed, e.g., noble metals on halogenated aluminas, exemplary of which is platinum on chlorided alumina.
In an alternate step in the process described by reference to (C), i.e., (5C) (iii), three-ring aromatics are catalytically cracked at catalytic cracking conditions to produce gasoline, or gasoline blending components. This reaction is carried to with a conventional "cat" cracking catalyst at conventional "cat" cracking conditions with, e.g., a zeolite cracking catalyst, encapsulated Y zeolite, silica-alumina or the like. Typical and preferred catalystic cracking conditions vary within the ranges given in Table 3.
TABLE 3 ______________________________________ Catalytic Cracking Conditions Typical Range Preferred Range ______________________________________ Temperature, .degree.F. 900-1050 950-1025 Pressure, psig 10-50 15-40 Residence Time, Sec. 5-120 10-15 Catalyst/Oil Ratio 3-10 4-8 ______________________________________
The invention will be more fully understood by reference to the following demonstrations and examples which present comparative data illustrating its more salient features. All parts are given in terms of weight except as otherwise specified.
A commercial BASF-R fused iron ammonia synthesis catalyst was employed in conducting the tests and demonstrations described in the text. The iron catalyst was received as prereduced, passivated small particles. This particulate catalyst was further ground and screened into smaller particles (14/35 Tyler mesh size) and then further reduced by contact with hydrogen prior to use. The chemical and physical properties of this catalyst on an as-received basis is given in Table 4, as follows:
TABLE 4 ______________________________________ Chemical Composition and Physical Characteristics of Commercial Fused Iron Catalyst (as received) BASF-R Catalyst ______________________________________ I. Chemical Composition, Wt. % FeO &lt;1 Fe.sub.2 O.sub.3 &lt;1 Free Fe 90-95 Al.sub.2 O.sub.3 2.0-3.0 K.sub.2 O 0.5-1.0 CaO 0.5-1.5 SiO.sub.2 &lt;0.5 P Trace S as SO.sub.3 Trace Chloride &lt;10 ppm II. Physical Characteristics Bulk Density 120 lb/cu ft in reduced form ______________________________________
In conducting these runs, where an iron catalyst is used, a small I.D. stainless steel tubular reactor was employed, the feed and hydrogen having been cocurrently introduced into the bottom of the reactor and passed upwardly over a fixed bed of fused iron catalyst centered within the reactor. In introducing the feed, a single piston, positive displacement pump was used to introduce the feed, admixed with hydrogen, into the bottom of the reactor. A sandbath was employed to heat the reactor. The temperature of the reaction was measured by a thermocouple located on the reactor next to the catalyst bed, and controlled by the use of an automatic temperature controller in operative association with the sandbath heated externally by resistance heaters. The feed mixture was heated in transfer line prior to entry into the catalyst bed. Products exiting the reactor were condensed and collected in a receiver cooled to about 32.degree. F., and a back pressure regulator was employed to maintain the desired pressure in the reactor.
The product collected from the reactor was analyzed by (1) a gas chromatograph (G.C.) distillation technique, (2) NMR to measure hydrogen content, (3) X-ray fluorescense to measure sulfur content, (4) high pressure liquid chromatography to measure aromatics content, (5) Antek procedure to measure nitrogen, and (6) mass spectrometry (MS) to analyze the off gas. Some selected products were analyzed by liquid mass spectrometry.
The feed of choice for conversion over the fused iron catalyst to make motor gasoline is one which is rich in tetralins or tetralin derivatives which can be converted over an iron catalyst at proper conditions to alkylbenzenes in high yields, providing a product of high octane value. Paraffins, decalins and naphthalenes at low concentrations are essentially unreactive in such reaction. this is demonstrated by the example immediately following.